story: Height above average terrain (HAAT) (or less popularly, EHAAT, Effective Height Above Average Terrain) is a measure of how high an antenna site is above the surrounding landscape. HAAT is used extensively in FM radio and television, as it is more important than effective radiated power (ERP) in determining the range of broadcasts (VHF and UHF in particular, as they are line of sight transmissions). For international coordination, it is officially measured in meters, even by the Federal Communications Commission in the United States, as Canada and Mexico have extensive border zones where stations can be received on either side of the international boundaries. Stations that want to increase above a certain HAAT must reduce their power accordingly, based on the maximum distance their station class is allowed to cover (see List of North American broadcast station classes for more information on this). 
  
  The FCC procedure to calculate HAAT is: from the proposed or actual antenna site, either 12 or 16 radials were drawn, and points at 2, 4, 6, 8, and radius along each radial were used. The entire radial graph could be rotated to achieve the best effect for the station. The altitude of the antenna site, minus the average altitude of all the specified points, is the HAAT. This can create some unusual cases, particularly in mountainous regions—it is possible to have a negative number for HAAT (the transmitter would not be located underground, but rather in a valley, with hills on both sides taller than the transmitter itself, for example).
questions: What does HAAT stand for?
questions: What is a similar acronym that means the same thing?
questions: Can it be a negative number?
questions: Where does that happen?
questions: What industries is it used in?
questions: What transmission types?
questions: Is it given in feet?
questions: What unit is used?
questions: Why?
questions: What is subtracted from what to find it?
answers: It stands for Height about average terrain
answers: Height above average terrain 
answers: The less popular version, EHAAT, Effective Height Above Average Terrain
answers: EHAAT, Effective Height Above Average Terrain
answers: Yes
answers: it is possible to have a negative number for HAAT (the tra
answers: Usually in the mountainous regions
answers: his can create some unusual cases, particularly in mountainous regions—
answers: More commonly, FM radio and television
answers: extensively in FM radio and television, 
answers: Usually VHF and UHF
answers: VHF and UHF in particular,
answers: NO
answers: it is officially measured in meters,
answers: Meters
answers:  it is officially measured in meters, 
answers: So that stations can be recieved on either side of the international boundaries.
answers:  as Canada and Mexico have extensive border zones where stations can be received on either side of the international boundaries. 
answers: average altitude
answers: the average altitude of all the specif